This is an application to the National Institute of Alcohol Abuse and Alcoholism for a Senior Scientist Award (K05). The candidate, Barbara C. Leigh, Ph.D., MPH, a Senior Research Scientist at the Alcohol and Drug Abuse Institute at the University of Washington, proposes to continue her ongoing program of research on substance use and HIV risk behavior. Goals for this five-year period include a) investigating the relationship of substance use to HIV risk behavior from a methodological perspective, incorporating person-level, event level, and within-person analyses;b) studying the association of alcohol and other drug use to risk behavior in a national sample of adolescents;and d) developing new projects to expand research in both these areas. The career plan also includes continued collaboration with local and international colleagues in scientific activities, and expansion of mentoring and science education. By providing Dr. Leigh with stable funding and relieving her from reliance on short-term mechanisms of support, the award will allow her to sustain a programmatic line of research over the long term.